I have created a website that requires hotels/lodges to join and market their properties on. I need a letter of introduction that will influence the hotels/lodges to join the website and market their properties via the website. Please write for me the best letter I can get in order to send to the hotels/lodges.

First, we will not write such a letter for you. If you want someone to write the letter for you, I suggest hiring a PR firm. But we may be able to help you create one.

What advantages are there to a hotel to list on your site? How much traffic does your site get? What do you offer over similar sites?

Letters of introduction have gone the way of the dinosaur. Everything now is keywords.
Hotels have their own websites, and there are countless sites like yours. If you don't have something new, it's not going to attract anyone.
Perhaps a LOCAL site for your area, including all attractions - lodgings, food, entertainment, history, arts.